On a New Torque Sensor for Compliant Grasp by Robot Fingers with a Tendon Actuation System

Summary

This paper discusses a new torque sensor for a compliant grasp by robot fingers. For finger joint actuation, a tendon driving sytem has normally been used, and a joint torque sensor is indispensable for controlling finger tip stiffness. However, it seems that a satisfactory torque sensor has not yet been developed for such a driving system. To cope with this, the authors propose a Tension Differential type Torque sensor (TDT sensor). The working principle of the sensor is demonstrated with comparisons of conventional approaches. To explore the stability of the torque servo system, the equivalent angular stiffness of the TDT sensor is formulated, and a loop gain σ is introduced for the case in which an arm having negligible moment of inertia is in contact with an environment. It is shown that through experiments, the loop gain σ is very useful for estimating the system stability. The basic design strategy of the TDT sensor is also considered from the viewpoint of insensitivity to a change of environment stiffness.